Pre-flowering and post-flowering insecticide applications to control Aphis fabae on field beans: their biological and economic effectiveness

Most spring-sown field beans are treated with insecticides to control Aphis fabae, but there is usually a risk of toxicity to pollinating honeybees if insecticides are applied during flowering. An experiment was repeated at Rothamsted for 6 consecutive years, comparing treatments before and after flowering. It is concluded that (1) pre-flowering treatments (demeton-S-methyl spray at 0–25 kg a.i. ha^-1 or phorate granules at 1–12 kg a.i. ha^-1) were more effective and profitable than post-flowering treatments, (2) application of phorate granules before flowering gave the greatest economic return, and minimised the danger to foraging bees and (3) aphid populations varied considerably from year to year, as did the relationship between aphid infestation and yield, but our evidence supports the suggestion that insecticide spray treatments are profitable if 5% or more of the plant stems are infested at the end of primary aphid migration.